Gas sensors are used in many commercial and industrial applications, including workplace monitoring for the presence of toxic or otherwise hazardous or deleterious gases and in other applications where health and safety issues require detection of specific gases in the ambient environment.
In these various applications, it is frequently necessary to monitor concentration of selected gas species down to levels of a few parts per million and less. In doing so, there is usually a need to remove, from the sampled air, other gases or volatile organic compounds that would likewise react at the sensor and generate an unwanted response. These gases normally have a myriad of different chemical properties, which therefore requires the use of a multitude of chemicals to remove each of them. For example, high surface area carbon is frequently used to adsorb most organic volatile species but the carbon is not effective at removing some of the common industrial inorganic gases. Thus, a second type of chemical must be used to remove those and so on. Typically, the carbon is coated with the second type of chemical or the two chemicals can be mixed then impregnated onto a solid support. Such an arrangement can quickly become self-destructive as the chemicals cross-react with each other, leading to decreased efficiency and longevity of the filter and gas sensor.
Gas sensors used in the foregoing applications include electrochemical gas sensors, which may operate to electrochemically reduce the gas species to be monitored. Alternatively, the gas sensor may operate by electrochemically oxidizing the target gas species sought to be detected. As a still further alternative, the electrochemical gas sensor may operate by indirect oxidation or reduction reaction of a compound that is produced in the gas sensor device involving the target gas to be detected in the monitored gaseous environment.
Electrochemical gas sensors utilize sensor cells that typically contain three electrodes—the working electrode, the reference electrode, and the counter electrode, although gas sensor cells are known having two-electrode and four-electrode structures. The electrodes are conventionally mounted within a housing that additionally contains an electrolyte, contacts, and electrical wires forming electronic circuitry of the sensor, and a gas permeable membrane that keeps the electrolyte within the cell and allows the gas to contact the measuring electrode.
Electrochemical sensor cells require an electrolyte as a component of the electrochemical cell. The electrolyte performs the transport of electrical charge between the different electrodes and therefore enables an electrical current to flow. The transport of electrical charge by the electrolyte is ionic in character rather than involving charge transport by electrons.
Conventional gas sensors contain filters that often use mixtures of chemicals to achieve multiple functionalities. Such gas sensors can have a limited lifespan due to the chemical components of the sensor reacting with each other or otherwise degrading due to environmental factors. The art therefore continues to seek improvements in electrochemical cell gas sensors. The current gas sensor comprises a novel filter that separates these materials into isolated chambers, which removes the risk of cross-reactions leading to improved overall filter efficiency and life without greatly increasing the complexity of the design.